(Not Applicable)
1. Background Field of Invention
This invention applies to the computer magnetic tape data recorder product industry and more specifically to the development of the mechanical tape (media) path portion of the product. However it can be applied to any industry that rolls webs of any width onto reels for further processing or storage purposes.
2. Background Prior Art
A search of the U.S. Patent Office Patent Records does not reveal a Roller Guide Assembly of any design that incorporates an integral Centrifugal Air Pump within it""s basic outline. The Durbeck U.S. Pat. No. 3,078,022, entitled FLUID BEARING, which was issued in 1960 was the only patent found that utilized a rotating pump to generate air flow to an Hydrostatic air bearing assembly. Looking at FIG. 1-PRIOR ART one can see the use of a Reaction Air Pump in this patent to push air into the air bearing insides. This patent teaches the problem with air bearings that uncovering ports that feed the air film generated can affect the operation of the bearing supporting a film. It teaches the use of a vane-like wall that does not rotate with the pump itself. But rather it is selectively positioned to cover the air bearing ports that may be uncovered depending upon the wrap angle of the media. The wrap can change when media is transferred from reel to reel during the data recording or reproducing process. The outside air bearing surface does not rotate. The wall position is controlled by a separate mechanism to set it where desired. It is believed that this pump design will not easily push air into the air bearing because of long, narrow air passages shown in FIG. 1. It is a very complicated design and there would be problems placing the design into any medium, or smaller sized, magnetic tape recorder. It is not obvious how to conceive of the Present Invention (described herein) based upon the Durbeck patent.
The only other patent that touches upon the Present Invention is the DAVISON et al U.S. Pat. No. 3,122,295, entitled WEB TRANSPORT, issued in 1964. The Davison Patent teaches driving 2 rotating capstans continuously using a single motor, belt and pulleys; in both CW and CCW directions at the same time. The function of the magnetic tape unit that uses this system is to allow the capstans to spin up to speed and hold this speed for the duration. Then a brake between the capstans is applied fully at all times. To start the media in either direction an external air pressure source is engaged to push down upon the media being supported by a Hydrodynamic Air Film generated by the spinning wheels. The two Capstan""s outer surfaces that the air film is generated upon have ports and exterior grooves. There are also a ring of sub-tunnels leading from these ports to the atmosphere at the sides of the wheels. The Patent states that the air film is allowed to collapse when the overhead air pressure is applied so the friction would cause the media and the capstan of choice to move together. No vacuum or pressure head is generated inside these capstan wheels. It teaches that the ports on the Capstan surface are exposed to atmospheric pressure through the surface grooves that intercept the ports, down through the cross-holes to the side. It teaches the fact that Hydrodynamic air film can be generated on a moving roller shaped surface but can be easily deflated by a design described in the Davison Patent. It does very effectively teach the use of an external motor and belt system to continuously rotate the subject wheels continuously. It does not teach the generation of Hydrostatic Air Films.
There are many examples in the U.S. Patent Record that teach both Hydrodynamic Air Film effects and Hydrostatic Air Film effect, but not at the same time. It may be possible that the Davison Patent does generate some Hydrostatic Air Film while rotating but it is not obvious. There is no effort to make the internal holes large enough or the internal spaces large enough so air could easily flow from the sides to the surface ports. The surface grooves would destroy any Hydrostatic Air Film with the bleeding off the pressure that may be generated. In fact it is hard to understand how even a Hydrodynamic Air Film could be generated with this invention.
A discussion of the difference relative to Magnetic Tape Unit design of Hydrodynamic and Hydrostatic pressures is presented here as an aid to understand the Prior Art better. Hydrodynamic Guides are very smooth guiding surfaces with very small wrap angles of the media entering and exiting the guide. They self generate an air film by pulling air into the space between the media supported over the guide and the guide exterior surface. The Hydrodynamic Principle applies to both when the guide is fixed, or if it rotates as in a roller design. The pressure is positive for a time before exiting the guide and at the trailing end it goes negative for a short time before the media leaves the surface. This is shown in FIG. 6-PRIOR ART. This figure shows a Hydrodynamic Guide supporting media traveling (V) across the top surface. Below, in FIG. 9 is a plot of the pressure developed in the interface between the media and guide surface. One can see the vacuum being generated at the left side due the conservation of energy that takes place during this operation. This vaccum causes contact between the media and roller surface. Note that the Pressure Area Al Equals A2. The pressure head (P) generated with this kind of guide is a direct function of speed of the media (V), tension of media moving across (T), radius of the guide (R), and the wrap angle (W) of the media being stretched over the guide""s top surface. An important aspect of using a Hydrodynamic Guide is to insure that the Wrap Angle is not too high. This would lead to stiction in high humidity conditions for the recorder and would produce operational errors for the machine. Also very small wrap angles will just fly the media over the guide surface without making contact. This might be preferable in tape unit design but probably not possible due to space limitations where the media must leave a reel and be wound up onto another reel in a very small space.
Hydrodynamic Guides are beneficial because of:
1) the Recorder Design can make severe direction changes when placing the tape path design into a small volume,
2) have been lower cost (up to this Invention) to use in low cost Tape Recorders, and
3) are simple in design and higher in reliability than air bearings (again up to this Invention).
A Hydrostatic Air Film is created when external pressure is applied to the insides of a guide with a number of small ports allowing the pressurized air to bleed to the top surface. If there were media with tension placed upon this surface then the bleeding air would be trapped and would develop a pressure. The U.S. Patent Record has numerous examples of Air Bearing design and improvements over the past 30 years, and it is a common, well know phenomena. The actual pressure generated in the space between the media and the guide outer surface is a direct function of the:
1) external supply pressure head,
2) the amount of air flow through the bearing ports due to leakage,
3) the tension applied to the media,
4) the wrap angle of the media,
5) are there any uncovered air bleed ports?, and
6) the amount of side leakage at the media edges.
In a Magnetic Tape Recorder it is preferable to use Hydrostatic Air Bearings as they allow:
1) little, or no, friction in the tape path,
2) do not engage the inertia properties of rollers that lead to tension spikes with starting and stopping the media,
3) do not have problems with any environmental conditions that would tend to produce humidity generated friction buildup between media and guide surfaces, and
4) will result in low power consumption for the entire recorder. Continuing with the Prior Art found in the U.S. Patent Record STAHLER""s U.S. Pat. No. 4,337,885, entitled APPARATUS FOR GUIDING TAPE, and issued in 1982, is shown in FIG. 3 PRIOR ART. It teaches how one would guide the recording media for improved Track Density across the media width by incorporating a slight Taper shown as the angle xe2x80x98Xxe2x80x99 in the FIG. 3. This possible guide system was never a viable design possibility for a Tape Recorder using a number of Rollers in the Tape Path layout. This is because of the Roller running with the moving media would make contact with the media and a significant frictional force could be present. It is impractical to guide against this frictional force as the guide forces would have to be large enough to overcome. The wrap angle and Tension applied to the media on the Roller itself provides a normal force that this frictional force results. This would lead directly to high edge forces and stresses on the media edges during operation. The result is edge damage and possible lost of data. As can be seen with the Stahler Patent, it is using a Hydrostatic Air Bearing to support the media. Very little force would be required to push the media so it would register against a valid guide surface as shown in FIG. 3. The Present Invention would allow a tapered surface to be used to guide the media towards a Reference Surface for increased Track Densities. This would negate slitting tolerances of the media and bearing Non-Repeatable Runout tolerances.
As was stated earlier in this section there was no instance in the U.S. Patent Record of a Roller using the principles of Centrifugal Force to generate a Hydrostatic air film. The best example of a straight-forward look at how a Centrifugal Fan operates is shown in FIG. 4 PRIOR ART. MacLeod""s U.S. Pat. No. 4,565,495, entitled ARMORING SYSTEM FOR AN AIRFOIL CENTRIFUGAL FAN, issued in 1986, shows how the air flows through a device incorporating Vanes. The FIG. 4 shows the Input Airflow (Gi) migrating through the unit and exiting at a angle normal to the centerline of the fan with Output Airflow (Go). The Vanes are an important aspect and essentially the fan would not perform well without them. Also the Inlet Shroud shown keeps the air directed so there is no appreciable leakage anywhere. This is important in order to generate sufficient pressure head with the flow. FIG. 7-PRIOR ART depicts a Pressure-Flow Curve for a typical Centrifugal Fan operating at a fixed speed. Note that when the Flow (Q) is reduced to near zero, then the Pressure (P) is at it""s maximum possible value. This tendency would apply to the Present Invention also. The Pressure Head inside the Roller and Integrated Pump would also be near it""s maximum due to media being held tight across most of the holes. Also note that the relationship indicated by the line plotted in FIG. 7 shows the relationship between Pressure and Flow is Non-Linear. This is due to the fact that the cross-sectional shape of the vanes that turn the air outwards do influence how efficiently it can be done with any fixed speed. This Non-linear relationship is the key to designing an efficient fan. Consequently the air-flow performance that is obtained on the Present Invention can be influenced greatly by the shape of the Walls (Vanes) cross-sections located on the inside surface of the Outer Tube of the Roller Assembly.
The exact path and pressure profile that an air flow device would follow cannot be analyzed and determined before actually building the device and testing it. Reference is made to the classic book titled, CHAOS, by James Gleick published in 1987 where the author discusses the inability of scientists to forecast the nature of fluids. More specifically his remarks on pages 121 through 123 where he describes how difficult forecasting the performance of an aircraft wing, and further discussions about xe2x80x98eddyxe2x80x99 currents in fluids that impact the final flow performance of any device using fluids. The development of air bearings has been mainly through building parts and testing them for performance. FIG. 8 PRIOR ART shows a typical example of a U.S. Patent (FIG. 1 of HAWLEY et al U.S. Pat. No. 3,984,039 issued in 1976) on the subject of Hydrostatic Air Bearings. It is representative of all the Air Bearing Patents that can be found in the Patent Record. None were found where the outer air bearing surface with the bleed ports on the surface were found that also rotated about it""s projected centerline based upon the radius selected for the bearing. The Davison Patent (discussed earlier) was the closest by spinning Hydrodynamic Capstan Wheels.
There are a number of Patents in the U.S. Record that show that the flow of lubrication, whether it is gas or fluid, can be influenced by the shape of the internal walls and structure. FIG. 5-PRIOR ART shows AGRAWAL""s U.S. Pat. No. 4,747,705, entitled POWER SHAPED MULTIPAD HYDRODYNAMIC JOURNAL BEARING, issued in 1988, where a complex shape is incorporated within the internal structure of a Bearing. There are others also and they are listed below. However it is not seen that these Patents teach the uniqueness of the Present Invention is any manner even though they teach the ability to enhance gas or fluid flows with Geometric shapes. The other patents found are:
All of the above referenced Patents have unique Geometric features for various types of bearings, however they do not teach the fundamentals put forward by the Present Invention.
Today""s magnetic tape data recorder product demands much lower costs and better reliability than earlier tape products. Also the Form Factor (the overall size of the product""s shape and size) enters into the market equation as xe2x80x98smaller is betterxe2x80x99 due to the reduction in space needed for computers of all models and cost targets. Today""s developers must use only roller guides to meet these demands. Hydrostatic air bearings require cost and space to be incorporated into small Form Factor tape units. And Hydrodynamic air bearings have unique problems also. Rollers work well in small spaces except as recording parameters such as Track Density (Tracks per Inch across the width of tape) go up for increased tape cartridge or tape reel data capacities, they do not lend themselves for accurate guiding. Also the roller introduces some new tension control aspects not seen before with increases in Recording Linear Densities (Flux Reversals per Inch along the length of tape). Increased capacity of the unit of media (either cartridge or reel) for a family of magnetic tape products is the single biggest aspect from a mechanical development viewpoint. Utilizing air bearings in a tape path add costs and complexity, however air bearings are a better component for controlling media guiding and tension control. The Roller-Air Pump concept discussed in this Specification provides the advantages of both the roller and the air bearing but not their weaknesses.